Preheat oven to 425 degrees.
Lightly grease a 12 cup muffin tin.
In a large bowl combine the flour, sugar, cocoa powder, baking powder, and salt.
In a medium bowl blend the banana, oil, eggs, and vanilla together.
Stir in wet mixture until just blended.
Spoon the batter into the prepare muffin tin, 3/4 full.
Bake in the preheated oven for 15 to 20 minutes.
Remove muffins to wire rack to cool completely.